[Hammarlund] Re: Signal Generators and Shielding

[Barry L. Ornitz]

David Edsall, W1TDD, <dedsall@crocker.com> noted:

> re: alignment of receivers, some signal generators have 
> an auxiliary hi-level output which is ideal for 
> connection to a frequency counter, and independent of the 
> calibrated output to the receiver.  You can set the
> frequency dead on, and set the attenuator output to any 
> level you wish.  The HP 606A or B models and the URM-25 
> both have this feature.

Just remember than many inexpensive frequency counters are 
not shielded very well.  Thus if you are trying to 
determine the sensitivity of a receiver and need signals 
levels below 10 microvolts or so, you probably need to 
remove the connection to the counter and place a cap over 
the high-level output jack.

I have seen too many Boatanchor restorers report the 
sensitivity of old receivers to be far better than what is 
really possible due to signal generator leakage.  When you 
get the generator turned down to 20 microvolts or less, 
watch the receiver S-meter to see if it continues to drop 
as the generator output is reduced.

While the HP-606 is well shielded and has a good 
attenuator, the URM-25 is often very different with many 
units having considerable RF leakage.

        73,  Barry L. Ornitz     WA4VZQ     ornitz@tricon.net

P.S.  While I am not trying to pick on David specifically 
here, please consider turning off automatic quoting of the 
previous message if you are unwilling to edit it out 
manually.  The entire digest was repeated in his message 
taking excess bandwidth and wasting the resources of our 
generous host.